Pfau Zeh is a Commodore VIC-20 emulator for Linux that runs nearly all VIC-20 software. Play your favorite cartridge games or code some BASIC programs. Hasn't been updated in quite awhile though, most likely discontinued...

VICE is a very good C64 emulator. It has great speed and good graphics and sound emulation. It has lots of options and runs most software for C64. It also emulates VIC20 and PET systems. This is a great download.